Sorry to put a damper on your plans Nigel, but in my view, it is not worth it. Le Tour is so much better enjoyed on the telly, in a pub, in a village en-fete on Bastille Day etc.
I apologise for the length of this reply in advance and, like everything in life, your mileage may vary...
We went to Barcelona to see the finish of stage 6 this year. We arrived at the finish line 3 hours before the expected finish time. The entire area was packed with people - the closest I got to the finish line was standing at the 150m marker 3 people back - I'm 6'4" so I at least could see the road.
There was a big screen, so I got to watch the race in the pouring rain (with no commentary). I was the only person around who seemed to care that there was a race on - people from all nationalities around talking about everything but cycling!
As the caravan approached the finish (about 60 minutes in front of the race), everyone surged forward to get their hands on the rubbish and tat being dumped by the caravan. So suddenly everyone is wearing white Skoda hats and yeloow Creid Lyonais hats (both at the same time!), waving green PMU foam hands and munching on Haribo.
Then le Tour arrives - the sprint (uphill in this case) was so fast that it made my eyes water (or was it just the rain?). We tried to take a photo of the lead rider (Thor Hushvod, in this case) and only managed to capture the rider who finished 10th (see photos below). The finishes are really that fast!
As soon as the race finished, the crowds moved (ran/pushed) to the podium area, packing in as close as possible to see the podium ceremonies.
Then it is all over. The crowds walk away, leaving the ground covered in empty bottles and cans, food wrappers and discarded advertising tat. There were no bathroom facilities whatsoever on Mont Juic, so lots of people were racing back up the hill to the Funicular station!
We were there at 9:30am the next day for the sign-on and depart (at 11:00am). We walked up the Avenue Parallel to Plaza de Espania to find the entire area fenced off with 2 metre tall metal fences. It was possible to walk around the area, but not through it and certainly nowhere near the riders, team buses, VIP areas etc.
We took up position to watch the sign-on. Riders came in dribs and drabs - anyone who could speak Spanish was 'detained' by the announcer for impromptu interviews - everyone else sort of sneaked onto the stage and sneaked off again as quickly as possible. If your French & Spanish wasn't up to a high standard, you would get very little out of the sign-on!
The worst for us was that both the finish of stage 6 and the neutralised start of stage 7 passed the window of our hotel. We could have got a much better view from our bedroom window, while watching the stages on TV, using our private bathroom and drinking ourselves silly. Instead, we left feeling that the glamour and spectacle so often described in cycling magazines, books and commentaries had been somewhat exaggerated!
Of course, it didn't help that the weather in Barcelona was bloody apocalyptic and that someone tried (and failed, after a hard chase) to snatch Mrs dmoan's handbag...